Calls are growing louder for a vote to override Governor Bruce Rauner's veto of the education spending bill.

The calls come as House Speaker Michael Madigan cancelled a legislative session Wednesday that was supposed to take up the vote. The session was cancelled because top lawmakers are making significant progress towards a compromise, but with questions about just what that deal might look like still very much unanswered, mayors and school superintendents made their voices heard Wednesday.

As students across the state head back to school, Chicago mayor Rahm Emanuel and the Metropolitan Mayor's Caucus were trying to turn up the heat on lawmakers to override the veto of Senate Bill 1.

"I don't know how much pressure we can exert, but we will try to exert as much as humanly possible to make sure this measure moves forward," said Park Forest mayor John Ostenburg.

"I think it's really unfortunate that you're the governor of Illinois and you've decided that the best political argument is for you to pit a child of Chicago against a child of any one of these cities," Emanuel said.

Rauner said he vetoed SB-1 because it took money away from poorer school districts to help pay for Chicago's massive pension liability. His veto would cost Chicago hundreds of millions of dollars. But as the battle over the funding bill drags on, some superintendents from poor downstate districts gathered to call for a veto override or a compromise that still helps Chicago.

"No red numbers for Chicago, for Sandoval, for East St. Louis, no red numbers for anybody," said Dr. Jennifer Garrison, superintendent for Sandoval School District 501.

"We ask that both parties put aside these differences for at least the next six days and get this thing done," said Chuck Lane, superintendent of Centralia High School.

A House veto override vote has been tentatively scheduled for next Wednesday, but talks among the top four legislative leaders continue. Tuesday's session in Speaker Madigan's office lasted more than five hours. House Republican Leader Jim Durkin called it the most productive round of discussions so far.

"I feel very confident that we are on a path to be able to reach a compromise to avoid having a, I would say, have a vote on SB-1, which I would say is unnecessary right now," Durkin said.

The top legislative leaders will meet again Thursday in Chicago. This will be their fourth meeting in the past week. One detail that has leaked out of the compromise is a Republican-backed $75 million school voucher program.